1. Field of the Invention
The present invention relates to a method for initializing optical data storage media, and more particularly to a method and an apparatus for initializing an optical disk of a phase transformation type in a short time therefor.
2. Description of the Prior Art
Optical media of a phase transformation type are utilized as multimedia data storage media because of their large capacity as well as their high portability and reliability. This type of media is composed of an optical disk of a phase transformation type and an optical disk reproducing unit.
An optical disk of a phase transformation type stores and erases data based on an irradiating of laser beams on a recording film to heat a substrate, thereby inducing a phase transformation between two crystallographically divided phases to record and erase data. Two phases have the separate reflectance, respectively, so that data is reproduced by detecting the reflectance variation. That is, data is recorded by using laser beams to reversibly transform the phase of the material use to fabricate the recording film, the data being read based on the difference in an optical characteristic(reflectance) between the phases(crystalline phase/amorphous phase).
In the phase transformation between amorphous and crystalline phases, the amorphous phase is obtained by using laser beams to heat the recording film material over its melting point and then rapidly cooling it, while the crystalline phase is obtained by heating the material over its crystallizing temperature.
This phase transformation typed optical disk has the advantage that purely optical systems are simplified because only optical devices are employed to read and erase data. Also, the disk is useful in digital moving picture recording and voice recording because the overwriting operation can be directly performed using a single beam to shorten the recording time. Further, data recording can be performed without a magnet which generates a magnetic field. Thus, the optical unit may be thin. Additionally, a light source having a short wavelength is employed to get a high densified unit.
More specifically, recording and reproducing can be performed only by laser beams, without a magnetic head to apply a bias magnetic field, because an external magnetic field is not required in a recording process. Thus, the optical system becomes simplified, effectively decreasing the production cost, increasing compatibility and decreasing thickness.
Further, recording and erasing operations are each performed by the power modulation of laser beams, so that the direct overwriting is possible.
Because reproducing signals are obtained based on the variations in the intensity of reflected light which is generated by the reflectance difference between the two phases, these optical storage media are very compatible with the read-only typed disk such as a CD(compact disk) and the write-once and read-many typed disk.
Hereinafter, the general manufacturing process of the phase transformation typed optical disk will be described.
A digital master tape is made by the digital processing through a digital console, and then a code encoding process is performed to insert the sub-code representing the information related to a disk and to cut the disk using laser beams.
Then, several drops of photoresistor are dropped during the rotation of a spinner on glass that is ground evenly and precisely and is cleaned ultrasonically. The photoresistor forms a coating that is about 0.1 um thick, depending upon the rotation number of the spinner and the viscosity of the photoresistor.
A glass master is manufactured by exposing and developing the photoresistor with argon laser (wavelength of 457.9 nm) or Hexe2x80x94Cd laser (wavelength of 441.6 nm).
A sheet of metal master is manufactured by plating the original photoresistor plate, and then several sheets of mother are manufactured. Several sheets of stamper are manufactured from the mother, and the stamper is subject to trimming to be provided for a molding device.
Next, as shown in FIG. 1, a polycarbonate substrate 1 is manufactured by injectedly molding the melted polycarbonate. A first dielectric layer 2, a recording film 3, a second dielectric layer 4 and a reflective layer 5 are stacked successively, and a protective layer(not shown) is formed thereon with the spinning technique to prevent the deterioration of film. Finally, a recording film is initialized, and the disk is tested to evaluate its quality.
The initializing process is necessary for the phase transformation typed optical disk, where the process of xe2x80x9cinitializingxe2x80x9d involves crystallizing a stacked recording film which is made of materials constituting the recording film by sputtering to have a thickness of 50 to 500 xc3x85 by heating that stacked recording film over the crystallizing temperature. FIGS. 2a and 2b are schematic views showing the pre-transformation and post-transformation atomic arrangements of the materials constituting the recording film of the phase transformation typed optical disk, respectively.
Japanese Patent Unexamined Publication Nos. sho 60-106031 and sho 62-250533 disclose the conventional initializing methods.
In Japanese Patent Unexamined Publication No. sho 60-106031, a method is disclosed for using a laser beam to successively heat the optical disk track-by-track from its inner circumference to its outer circumference Specifically, according to the publication, a first laser diode is used to read/reproduce data A second higher powered laser diode capable of obtaining a laser spot of several to several hundred micrometers in size (generally 0.5 to 1 micrometers) is used to initialize the optical disk by successively heating the disk track-by-track. As a result, the conventional method effectively reduces the initializing and preventing the occurrence of cracks because the track-by-track heating leads to the lower heat load. However, using this method, even the reduced initializing time is to long, i.e. overall, it requires 30 min. to 1 hour to initialize disk since the initialization is performed track-by-track. Therefore in case of mass-producing the disk, the productivity is reduced, and the manufacturing cost is increased.
In order to overcome the above problems, Japanese Patent Unexamined Publication No. sho 62-250533 discloses a method for crystallizing an entire region of a recording film simultaneously by irradiating that region with a flash of light from a lamp. First, to initialize, the disk is heates to a temperature that exceeds the crystallizing temperature by applying 1 MW of power for the exposing time of 500 us (i.e. with the heat energy of about 500 J. A xenon lamp is employed as a light source in the publication. The instant exposure induces the stress which curves the disk. The curved disk restores its flat shape by annealing a stacked plurality of the curved disk with the irradiated light from a mercury lamp. The initializing process is completed by re-initializing the disk which rotates at a high speed according to the method disclosed in the Japanese Patent Unexamined Publication No. sho 60-106031.
However, this method has the problem that an additional process for making the disk flat such as an annealing process is required, because the heat energy which is instantly and unevenly irradiated to the disk with the xenon lamp of a relatively high power curves the disk. Thus, the productivity is reduced and the manufacturing cost is increased.
The present invention is devised to solve the foregoing problems. It is an object of the present invention to provide a method for initializing a phase transformation typed optical disk and an apparatus therefor capable of enhancing the productivity as well as the yield by means of initializing the disk simultaneously to shorten the initializing time and minimize the deformation of the disk.
To achieve the above object of the present invention, a method is proposed which comprises the steps of, applying electrical energy to a recording film of a phase transformation typed optical disk to generate heat caused by an electric current flowing over the recording film, and
crystallizing the material constituting the recording film by heating the recording film to a temperature that exceeds the crystallizing temperature with the Joule heat.
According to an embodiment of the present invention, a method and apparatus are disclosed for initializing an optical disk by heating a recording film by directly contacting conductive wires to the recording film to apply an electric current over the recording film.
According to another embodiment of the present invention, a method and apparatus are disclosed for initializing a phase transformation typed optical disk by generating an induced current on the recording film by inducing heating without directly contacting conductive wires to the recording film, and heating the recording film with heat generated by the induced current.
A pair of the opposing conductive wires are connected to the inner circumference of the recording film of the optical disk through contacting parts, while another pair of opposing conductive wires are connected to the outer circumference thereof.
The initializing method according to the another embodiment of the present invention includes the steps of generating an induced current over a recording film by induction, and initializing a phase transformation typed optical disk with heat generated by the induced current.
The initializing apparatus according to the present invention for initializing a phase transformation typed optical disk having a recording film in which its optical properties are changed by the phase transformation comprises:
an electric source for applying a current;
conductive wires connecting a source of power to the recording film of the phase transformation typed optical disk;
contacts provided to the recording film and connected with the conductive wires; and
a switch for opening or closing an electric circuit having the source of power,
wherein a current is provided from the electric source if the switch is ON, the recording film being heated over its crystallizing temperature based on the heat generated by the current.
Further, the apparatus includes a high voltage alternating current (A.C.) source for applying a current, a switch for opening or closing an electric circuit having the A.C. source, and a heating inductance coil wound around the optical disk by a predetermined number of turns, wherein a current is provided from the A.C. source to the heating inductance coil if the switch is on, and wherein the recording film is heated over the crystallizing temperature by the heat generated by a current induced to the recording film by the magnetic flux generated inside the inductance coil.
The heat H is determined according to H=I2RT, wherein I is the induced current, R is the resistance of the recording film and T is the applied time of current.
The heat H is determined by the initializing temperature of the recording film that represent a temperature required to initialize the recording film, and the heat conductivity, and the like. The applied voltage and time are determined by electric properties of the material of the recording film such as the resistance.
Preferably, the material may be a Gexe2x80x94Sbxe2x80x94Te type alloy and a Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te type alloy, but the constituents of which are not limited as this.